The present invention relates to a molded plastic package for encapsulating a semiconductor device. More particularly, an anodized aluminum heat spreader is at least partially embedded in the molding resin enhancing the dissipation of heat from the device.
Molded plastic electronic packages provide environmental protection to integrated circuit devices. Packages such as the QFP (plastic quad flat package) and PLCC (plastic-leaded chip carrier) protect an encapsulated device from contaminants such as moisture as well as from mechanical shock. One molded plastic package is illustrated in U.S. Pat. No. 4,707,724 to Suzuki et al, which is incorporated by reference in its entirety herein. The package has a leadframe with a centrally positioned die attach pad. The semiconductor device is bonded to the pad and electrically interconnected to the inner ends of the leadframe. A polymer molding resin encapsulates the device, die attach pad and inner lead ends.
One disadvantage with molded plastic packages is poor thermal dissipation. During operation, the semiconductor device generates heat which must be removed to maintain the operating integrity of the device. While some heat is dissipated through the bonding wires and leadframe, the remainder is absorbed into the molding resin. The molding resin is a poor thermal conductor so the device temperature will increase unless the power provided to the device is limited.
Incorporating a heat spreader into the molded plastic package provides an enhanced path for thermal dissipation. As a result, more power may be provided to the semiconductor device without a resultant excessive increase in device temperature. The heat spreader, which is usually copper, is embedded in the molding resin, usually below the die attach paddle, reducing the amount of molding resin through which heat must pass to reach a surface of the package.
In addition to copper, heat spreaders formed from composites having a copper or aluminum component and a lower coefficient of thermal expansion component are disclosed in U.S. Pat. No. 5,015,803 to Mahulikar et al, which is incorporated in its entirety herein by reference.
Copper based heat spreaders provide good thermal dissipation, but do not adhere well to a molding resin and increase the weight of the package. Further, the copper catalyzes the degradation of some molding resins.
A method of improving the adhesion of a heat spreader to the molding resin is to form a plurality of grooves in the heat spreader to channel resin flow for mechanical locking as disclosed in U.S. Pat. No. 4,589,010 to Tateno et al. Alternatively, the copper is coated with a material having better adhesion to the molding resin as disclosed in U.S. Pat. No. 4,888,449 to Crane et al.
These approaches do not reduce the weight of the package and do not maximize the transfer of heat from a semiconductor device to a surface of the package.